The safety knife described in German Pat. No. 27 36 395 has a hollow handle body with a longitudinally slidable blade holder spring-loaded in the direction of the hollow knife handle.
The knife can be held in its working position with the blade extended, by an operating handle projecting outwardly, by transverse pressure applied by the thumb.
On release of the handle, the blade holder together with the blade is retracted into the hollow knife handle by a tension spring. This feature provides a substantial degree of safety from injury to the user. However the effort required to perform a blade change in a limited time interval requires improvement. This process should be performed more quickly than in the prior art safety knife. Also the construction of the known knife is relatively expensive so that it can only be used in advantageous applications where it has considerable advantage.